6.1 Expand Fault Tree

　

 To study detail of Fault Tree about unsafe navigation in extraordinary situation shown as Fig.5, we expanded Fault Tree on the basis of the Fault Tree of Fig.5 and analyzed the process under each fundamental phenomenon. Above-mentioned fundamental phenomena could be put as the top phenomenon and calculated Fault Tree structure importance. The expanded Fault Tree was shown as Fig.10.

　

6.2 Fault Tree structure importance about Expanded Fault Tree

　

　

　

　

　

　

 The calculated results except phenomena with lower importance are shown as table 3.

　

 There is "Insufficient Positioning before trouble" at two different places, and "Insufficient Lookout before trouble." is in the same way. Fault Tree structure importance of these phenomena was high. These two important phenomena, in addition to "Insufficient action to keep Positioning function" and "Insufficient recognition because of no Communication" could be expanded.

　

 Owing to these influence, Fault Tree structure importance are different depending on the Fault Tree structure importance of each top phenomenon. Importance under the phenomenon whose importance is high indicates higher value. The opposite is affirmative.

　

 "Insufficient Positioning before trouble" is caused by 4 phenomena; "Insufficient Positioning", "Insufficient estimate of external force and future situation", "Insufficient Planning to modify own position", and "Insufficient / Unsuitable execution to modify". Even if only one phenomenon among these phenomena happened, "Insufficient Positioning before trouble" would come. And its potential influence is larger, 0.038, than others.

 In the same way, "Insufficient Lookout before trouble" is caused by 4 phenomena; "Insufficient Lookout", "Insufficient estimate of situation" "Insufficient Planning for Lookout", and "Insufficient execution of Lookout". Even if only one phenomenon among these phenomena happened, "Insufficient Lookout before, trouble" would come. Its potential influence is also larger with 0.038.

 Both " Insufficient action to keep Positioning function" and "Insufficient recognition because of no Communication" would also come, even if only one phenomenon under each upper phenomenon happened. But its influence for occurrence of top phenomenon is not so large.

　

 From expanded Fault Tree, it is clarified that Fault Tree can be taken apart to some pieces, and then these pieces are concrete steps on the process to achieve an action.

 This also means that it is conceivable to be able to clarify the concrete cause by treating phenomenon individually on expanded Fault Tree in this way.

　

6.3 Steps in order

　

 Expanded part of Fault Tree consists of 4 steps. The process of thinking that human behavior passes 4 steps is well known. 4 Steps are recognition step, evaluation step, decision step, and execution step. Firstly the operator recognizes situation, and evaluates it whether it is necessary to react or not. Then the operator decides behaviour based on this evaluation, and executes that decision in conclusion.

 Therefore these steps should be done in order. If previous step were insufficient, it would bring bad influence on later step. From this point of view, these steps are expressed by Fault Tree shown as Fig.11.

 Sown as Fig.11, if Recognition was insufficient, it would bring bad influence on Evaluation. And then if Evaluation was insufficient, it would bring a bad influence on Decision. Unsuitable Decision occurs unsuitable execution of course. There is a flow of 4 steps.

　

　

6.4 Disturbance of 4 steps flow

　

 Flow of 4 steps in order means that only one insufficient / unsuitable phenomenon causes any disturbance on this flow process shown as Fig.11. And depending on its Fault Tree structure importance, that influence on the top phenomenon is large or small.

 Therefore, it is conceivable that, if we specified the phenomenon which causes unsuitable behaviour, we could obtain the countermeasure point suitably.

　

1) It could be clarified that what kind of phenomenon is important on the process by applying Fault Tree Analysis.

　

2) According to Fault Tree structure importance, the characteristic which 3 patterns of human behaviour in extraordinary situation is caused by how much the operator could achieve Positioning and Lookout before trouble is rational.

　

3) From this study, the necessary functions in ordinary situation was clarified, and then, even if the operator met the extraordinary situation suddenly, the operator would make it possible to recover from extraordinary situation in a short time as a result depending on achievement of function in ordinary situation.

　

[1] Uchino A., Kobayashi H., "Human Behaviour in Extraordinary Situations". Proceedings of INSLC- 12, California Maritime Academy, Vallejo, California, USA, 2002

[2] Kobayashi H., et al, "Developing of Ship-handling Techniques into Elemental Techniques and Proposal of Education / Training Methods Utilizing Ship-handling Simulator", Proceedings of IMIA 1997

　

 Akiko Uchino received a Master degree from Tokyo University of Mercantile Marine in 1994. From 1994 to 1998 she worked for Yusen Marine Science, Inc... She was engaged in developing ship handling simulator, research and education by ship handling simulator. From 1998 she in working for Tokyo Metropolitan College of Technology as research associate of department of Production Systems Engineering. She is a doctorial student of graduate school of Tokyo University of Mercantile Marine. Her subject is concerning about the human characteristics for information processing.